The immediate goal is to label differentially membrane proteins associated with the transport of glucose, amino acids and the Na ion-K ion transport system in human rbc and ascites tumor cells and to localize them on polyacrylamide gel electrophorograms. The differential labeling involves the use of alkylating agents which inhibit the transports and whose effects are partially blocked by transport substrates or transport inhibitors. This effect is used with double isotope labeling to differentially label transport sites.